Automotive vehicles are typically equipped with various user actuatable switches, such as switches for operating devices including powered windows, headlights, windshield wipers, moonroofs or sunroofs, interior lighting, radio and infotainment devices, and various other devices. Generally, these types of switches need to be actuated by a user in order to activate or deactivate a device or perform some type of control function. Proximity switches, such as capacitive switches, employ one or more proximity sensors to generate a sense activation field and sense changes to the activation field indicative of user actuation of the switch, typically caused by a user's finger in close proximity or contact with the sensor. Capacitive switches are typically configured to detect user actuation of the switch based on comparison of the sense activation field to a threshold.
Switch assemblies often employ a plurality of capacitive switches in close proximity to one another and generally require that a user select a single desired capacitive switch to perform the intended operation. In some applications, such as use in an automobile, the driver of the vehicle has limited ability to view the switches due to driver distraction. In such applications, it is desirable to allow the user to explore the switch assembly for a specific button while avoiding a premature determination of switch activation. Thus, it is desirable to discriminate whether the user intends to activate a switch, or is simply exploring for a specific switch button while focusing on a higher priority task, such as driving, or has no intent to activate a switch.
Capacitive switches may be manufactured using thin film technology in which a conductive ink mixed with a solvent is printed and cured to achieve an electrical circuit layout. Capacitive switches can be adversely affected by condensation. For example, as humidity changes, changes in condensation may change the capacitive signal. The change in condensation may be sufficient to trigger a faulty activation.
Electrical drift in the sensor signals can be caused by electromagnetic interference and internal drift caused by internal component interactions which typically happens very quickly. The magnitude of such electrical drift can be dependent on the circuit design and the intensity and frequency of the interfering radiation. The relatively quick change in the signal due to electromagnetic interference and internal drift interfering with the capacitive electric field may affect the ability of the capacitive sensors and switches to operate properly.
Accordingly, it is desirable to provide for a proximity switch arrangement which enhances the use of proximity switches by a person, such as a driver of a vehicle. It is further desirable to provide for a proximity switch arrangement that reduces or prevents false activations due to environmental changes such as condensation events, electromagnetic interference and internal drift.